1. Field of the Invention
The present invention relates to a cylinder apparatus that can lock a piston rod and a stabilizer apparatus for conducting roll control for vehicles by using the cylinder apparatus.
2. Description of the Related Art
In suspension apparatuses for vehicles etc., a torsion-bar type stabilizer has been used for roll suppression of a vehicle body when the vehicles are in a turning state. In the torsion-bar type stabilizer, each of right and left suspension arms that support wheels is connected to a torsion bar which is rotatably supported on a vehicle body. When strokes of the same direction are applied to the right and left suspension arms (when the strokes are “in-phase”), a spring force is not generated because there is no rotation of the torsion bar. On the other hand, when strokes of reverse direction are applied (when the strokes are “in anti-phase”), the spring force is generated by torsion of the torsion bar.
With this architecture discussed above, in a state where the vehicle moves in a linear direction, the spring force of the torsion bar becomes low thereby easily absorbing vibratory inputs from a road. On the contrary, in a state where the vehicle is in a turning state, the spring force is generated by torsion of the torsion bar so as to enhance roll stiffness, contributing to improvement of driving stability.
As disclosed in Japanese Patent Application Laid-Open No. 2005-178472 (hereinafter referred to as the patent document 1), the following stabilizer apparatus is known. A hydraulic cylinder is connected between a torsion bar and one of suspension arms. By locking or unlocking an operational rod of the hydraulic cylinder, transmission of spring force generated between the torsion bar and the suspension arm can be turned ON and OFF. With this architecture, it is possible to properly turn ON and OFF operation of the stabilizer according to vehicle driving conditions, contributing to better ride quality and driving stability.
In the hydraulic cylinder of the stabilizer apparatus disclosed in the patent document 1, a piston is slidably fitted into a cylinder in which a hydraulic liquid is filled, and a piston rod connected to the piston is extended outside from both end sides of the cylinder. Further, an opening and closing valve is provided at a communicating passage which communicates two cylinder chambers divided by the piston. With this architecture, by separating or communicating those two cylinder chambers by means of the opening and closing valve, it is possible to lock or unlock the stroke of the piston, and, that is, the piston rod.
As discussed above, since the piston rod is made extended from both end sides of the cylinder (a double rod structure), there is no volumetric change of the cylinder relative to the stroke of the piston rod, whereby no reservoir is necessary to be provided.
However, in the conventional stabilizer apparatus disclosed in the patent document 1, there are the following problems. That is, since the stabilizer is not provided with the reservoir, it becomes difficult to obtain temperature compensation for thermal expansion of the hydraulic liquid. In addition, since the stabilizer is structured as the double rod structure, the hydraulic cylinder may become too long.